Several thousands of years ago, the human species evolved from a hunting society in which food had to be captured and people constantly traveled in pursuit of food, to a farming society in which their nomadic existence ceased and settlement was made in areas of plentiful water or precipitation. At this time, the total number of humans which inhabited the earth was relatively low so that settlements could easily be made in favorable locations for the growing and production of food.
However, the worldwide population explosion of the last 200 years has forced people to inhabit areas which are less than hospitable for the production of food. Typically, farming communities have moved further and further away from a source of running water or precipitation in the form of rain and snow. Man, with his ingenuity, has compensated for this lack of natural water by producing many types of irrigation systems in which water is transported over a long distance through pipes, culverts, conduits or similar devices for the purpose of drip or area irrigation. Historically, these systems were rather crude since they did not allocate a specific amount of water to each plant or area based upon the needs of the crop or the amount of precipitation which had recently fallen in the area.
Consequently, a number of systems have been developed in which automatic irrigation and sprinkling systems water lawns and crops, based partly upon the amount of precipitation which has fallen on a particular area. Typical systems of this type are described in U.S. Pat. Nos. 2,776,860 issued to Griffis and 2,991,938 issued to Norcross. Both of these patents accumulate rain water in various containers and disable an irrigation solenoid valve until the water accumulated in these containers is eliminated. Specifically, the water accumulated in the Griffis patent is eliminated in a gradual nature, whereas the water accumulated in the Norcross container is eliminated in a series of discrete drain events. Therefore, if an irrigation event, i.e., the sprinkling of water in a large area or drip irrigation to a specific plant, is scheduled when water is still contained in the container, this irrigation event will be partially or completely cancelled. Although the systems do operate in a manner to save water or to prevent over-watering, these systems do not always operate in an efficacious manner, especially when several irrigation events are immediately proceeded by a rainfall.